Every year approximately 20 million pounds of extruded or calendared sheets are used to make automotive interior parts such as door panels and instrument panels in North America alone. Generally, the interior parts can be prepared from the extruded sheets by various known plastic processes such as thermoforming. Currently, most of the extruded sheets are made of flexible polyvinylchloride (f-PVC) and thermoplastic polyolefin (TPO) and the f-PVC and TPO sheets are generally top-coated with polyurethane (PU) coatings to keep the gloss of the post-thermoformed parts low (e.g., <about 6% at 60 degree) for consumer safety reason and to increase scratch resistance. In general, the use of PU coatings is not desirable because of their high volatile organic compound (VOC) emissions, and interference with grain pattern replication in the f-PVC and TPO sheets. Therefore, suppliers of automotive parts are always looking for alternative materials with low gloss. Attempts to use alternative polymer compositions such as blends of elastomers and polyolefins such as polypropylene are often not satisfactory because the gloss of the extruded sheets is generally high and the scratch resistance is generally low.
Every year approximately 30 million pounds of extruded profiles using low gloss thermoplastic vulcanizates and over 700 million pounds flexible profiles are produced using high gloss polyvinyl chloride (PVC). There is a desire for suppliers to keep low gloss and use lower cost alternatives. Attempts to use alternative polymer compositions such as blends of elastomers and polyolefins such as polypropylene are often not satisfactory because the gloss of the extruded profile is generally high and the scratch resistance is generally low.
Therefore, there is a need for novel polymer compositions that are thermoformable and/or extrudable into shaped profiles and can meet the gloss and scratch resistance requirements for various applications such as interior parts for transportation industries such as the automotive industry. Specifically, there is a need for extruded sheets that (1) can be thermoformed into automotive interior parts that have a desirable gloss of less than 6%; (2) are substantially free of defects such as webbing, ripping, tearing, pin holes and the like; (3) exhibit improved scratch resistance; and (4) do not require PU coatings for gloss control. Further, there is a need for automotive interior parts made from novel polymer compositions that are thermoformable and possesses the desirable gloss properties.
The aforementioned needs are met by various aspects of the inventions. In one aspect, the invention relates to a polymer composition comprising at least one ethylene/α-olefin interpolymer and a polypropylene. In one embodiment, the polypropylene is a branched or high melt strength polypropylene. In another embodiment, the polypropylene has a melt flow rate of at least about 2, preferably at least about 2.5 g/10 minutes measured with a 2.16 Kg load at 230° C. according to ASTM 1238. In another embodiment, a polypropylene, preferably branched, has a tan delta value at 0.1 radians per second of less than about 2.5, preferably less than about 1.5, more preferably less than about 1.0.
In another embodiment, the ethylene/α-olefin interpolymer has a Mw/Mn from about 1.7 to about 3.5, at least one melting point, Tm, in degrees Celsius, and a density, d, in grams/cubic centimeter, wherein the numerical values of Tm and d correspond to the relationship:Tm≧−2002.9+4538.5(d)−2422.2(d)2.
In another embodiment, the ethylene/α-olefin interpolymer has a Mw/Mn from about 1.7 to about 3.5, and is characterized by a heat of fusion, ΔH in J/g, and a delta quantity, ΔT, in degrees Celsius defined as the temperature difference between the tallest DSC peak and the tallest CRYSTAF peak, wherein the numerical values of ΔT and ΔH have the following relationships:ΔT>−0.1299(ΔH)+62.81 for ΔH greater than zero and up to 130 J/g,ΔT≧48° C. for ΔH greater than 130 J/g,wherein the CRYSTAF peak is determined using at least 5 percent of the cumulative polymer, and if less than 5 percent of the polymer has an identifiable CRYSTAF peak, then the CRYSTAF temperature is 30° C.
In another embodiment, the ethylene/α-olefin interpolymer is characterized by an elastic recovery, Re, in percent at 300 percent strain and 1 cycle measured with a compression-molded film of the ethylene/α-olefin interpolymer, and has a density, d, in grams/cubic centimeter, wherein the numerical values of Re and d satisfy the following relationship when the ethylene/α-olefin interpolymer is substantially free of a cross-linked phase:Re>1481−1629(d).
In another embodiment, the ethylene/α-olefin interpolymer has a molecular fraction which elutes between 40° C. and 130° C. when fractionated using TREF, characterized in that the fraction has a molar comonomer content of at least 5 percent higher than that of a comparable random ethylene interpolymer fraction eluting between the same temperatures, wherein said comparable random ethylene interpolymer has the same comonomer(s) and has a melt index, density, and molar comonomer content (based on the whole polymer) within 10 percent of that of the ethylene/α-olefin interpolymer.
In another embodiment, the ethylene/α-olefin interpolymer is characterized by a storage modulus at 25° C., G′(25° C.), and a storage modulus at 100° C., G′(100° C.), wherein the ratio of G′(25° C.) to G′(100° C.) is from about 1:1 to about 10:1.
In another embodiment, the ethylene/α-olefin interpolymer has at least one molecular fraction which elutes between 40° C. and 130° C. when fractionated using TREF, characterized in that the fraction has a block index of at least 0.5 and up to about 1 and a molecular weight distribution. Mw/Mn, greater than about 1.3.
In another embodiment, the ethylene/α-olefin interpolymer has an average block index greater than zero and up to about 1.0 and a molecular weight distribution. Mw/Mn, greater than about 1.3.
In another embodiment, the α-olefin in the ethylene/α-olefin interpolymer is styrene, propylene, 1-butene, 1-hexene, 1-octene, 4-methyl-1-pentene, norbornene, 1-decene, 1,5-hexadiene, or a combination thereof.
The ethylene/α-olefin interpolymer characteristics above are given with respect to the ethylene/α-olefin interpolymer before any significant crosslinking, i.e., before crosslinking. The ethylene/α-olefin interpolymers useful in the present invention may or may not be crosslinked to a degree to obtain the desired properties. By using the characteristics above as measured before crosslinking is not meant to suggest that the interpolymer is or is not required to be crosslinked—only that the characteristic is measured with respect to the interpolymer without significant crosslinking. Crosslinking may or may not change each of these properties depending upon the specific polymer and degree of crosslinking.
In another aspect, the invention relates to articles such as thermoformed articles comprising the polymer composition disclosed herein. In one embodiment, the thermoformed article is an article for the transportation industry such as an interior or an exterior part for a automotive vehicle. In another embodiment, the 60 degree gloss of the surface of the thermoformed article is less than about 9.0%. In another embodiment, there is no visible scratch whitening on the surface of the thermoformed article after tested for its scratch resistance according to ASTM D7027-05 at a load equal to or less than 20 N and a scratch speed of 50 mm/s.
In another embodiment, the polymer composition or thermoformed article further comprises at least one additive, wherein the additive is selected from the group consisting of mold release agents such as a polysiloxane, a colorant or pigment, plasticizer, an oil, an antioxidant, a UV stabilizer, a filler, a lubricant, an antifogging agent, a flow aid, a coupling agent, a cross-linking agent, a nucleating agent, a surfactant, a solvent, a flame retardant, an antistatic agent, an antimicrobial, a scratch or mar resistance agent, or a combination thereof.
Additional aspects of the invention and characteristics and properties of various embodiments of the invention become apparent with the following description.